There are more than 325 million people living in big cities, sprawling suburbs and rural areas throughout the United States. A sweeping set of data from the Blue Cross Blue Shield Association (BCBS) is shedding light on the conditions impacting many of these communities and helping experts understand which health challenges are urgent and emerging.

The Blue Cross Blue Shield System (BCBS) created a first-of-its-kind metric for measuring Americans’ health from birth to age 64: The Blue Cross Blue Shield Health IndexSM. The BCBS Health Index highlights which illnesses — from major depression to substance use disorder —are lowering the quality of life of people across the nation.

What does “optimal health” mean and how is it measured?

Using a score between 0 and 1, the BCBS Health Index rates the “optimal health” of populations on the national, state and even county level. A score of 0.8, for instance, means a group of Americans are living at 80% of their optimal health. By focusing resources on addressing the top conditions impacting their county or state, that group of people could be 20% healthier.

The simplest way to understand the BCBS Health Index is to view the interactive map, which breaks down the complex data and shows overall health for each county by color — blue indicating higher health; orange showing lower health scores.

Americans' diets are associated with numerous health conditions, but improving what we eat can make a difference.(Photo: Rawpixel, Getty Images/iStockphoto)

The top 10 health conditions that have the greatest impact on Americans’ quality of life include:

1. Hypertension — National Health Impact 12.5%

More commonly known as high blood pressure, hypertension is “a common disease in which blood flows through blood vessels, or arteries, at higher than normal pressures,” according to the National Institutes of Health. Hypertension occurs when the force against the artery walls is too high, which can cause heart attack or stroke. It can be associated with advanced age, obesity, smoking and stress. Hypertension is also known as the silent killer because it has no early significant symptoms but creates an extra load on the heart and blood vessels.

2. Major Depression — National Health Impact 9%

Major depression, which frequently goes undiagnosed or untreated, is a mental illness characterized by a constant sense of hopelessness and despair, making it difficult to work, sleep or eat. The condition affects adults, teens and children.

3. High Cholesterol — National Health Impact 8.6%

When levels of cholesterol are too high, fatty deposits can begin to build up in blood vessels and arteries, restricting blood flow. High cholesterol, which can be hereditary or from the result of unhealthy diet and lifestyle choices, can increase the risk of heart attack and stroke.

4. Coronary Artery Disease — National Health Impact 7%

High blood pressure, high cholesterol, smoking and diabetes can all damage or injure the inner layer of coronary arteries. Over time, the damage can worsen and become coronary artery disease, putting you at much higher risk of heart attack.

5. Type 2 Diabetes — National Health Impact 5.5%

In people with diabetes, blood sugar levels rise higher than normal. Type 2 diabetes, the most common form of the disease, is caused by obesity and lack of physical activity in about 90% of cases in the U.S.

6. Substance Use Disorder — National Health Impact 3.4%

Also known as a drug use disorder, a substance use disorder involves an overuse of, or dependence on, a medication or toxin. Addiction can cause serious mental and physical injury, overdose and even death.

7. Alcohol Use Disorder — National Health Impact 3.3%

The National Institutes of Health define alcohol use disorder as a “chronic relapsing brain disease characterized by compulsive alcohol use, loss of control over alcohol intake, and a negative emotional state when not using.” Very high blood alcohol levels can result in coma or death, and withdrawal from alcohol can cause hallucinations or even seizures.

A chronic inflammatory lung disease, COPD causes airflow from the lungs to be obstructed. The primary cause of COPD is cigarette smoking.

9. Psychotic Disorder — National Health Impact 2.9%

People with psychotic disorders, including schizophrenia and delusional disorder, often have trouble maintaining a sense of reality. These disorders can have a significant detrimental impact on a patient’s quality of life.

10. Crohn’s Disease/Ulcerative Colitis — National Health Impact 2.7%

This chronic disease causes inflammation in the digestive tract. According to the National Institutes of Health, “Crohn’s affects your small intestine and the beginning of your large intestine. However, the disease can affect any part of your digestive tract.” This disease can lead to ulcers, abscesses, fistulas, malnutrition and more. In addition to being painful and debilitating, the condition can lead to life-threatening complications.

Differences in health can vary by geography, income level and education.(Photo: vgajic, Getty Images)

What the data tells us: Health issues vary widely by geography, education and income

The top 10 national health conditions fall into three groups: physical, mental and unique health conditions, which together paint a complicated picture of health in America.

There is a strong relationship between physical conditions and income. In places with lower levels of education and higher unemployment, physical conditions like high cholesterol, COPD and diabetes have a much greater impact.

Many people do not seek a diagnosis or receive treatment for mental illness. Major depression is diagnosed far more often in counties with higher rates of education, while more socioeconomically depressed counties with large minority populations experience some of the lowest impact from mental health conditions. That doesn’t mean depression is less common in those counties; it really means that, for a variety of reasons, more patients in those areas are going undiagnosed and untreated.

Some conditions are harder to anticipate and predict. Unique conditions — among them, substance use disorder — follow a less distinguishable geographic pattern. They are much less related to socioeconomic factors, and their impact from county to county may be tied more closely to the population’s access to treatment than to demographics.

Gaining a deeper understanding of America’s overall health and well-being is the first step toward improving it, and BCBS is working to put data-driven insights into the hands of policy makers, influencers and researchers. As we continue the conversations on pertinent topics that affect so many Americans — like the opioid epidemic, obesity, depression and heart disease — the BCBS Health Index can be used to make information-based, objective decisions about how to help our nation get healthier. To learn more about the health issues impacting your county or state, take a tour on the interactive BCBS Health Index map.

Members of the editorial and news staff of the USA Today Network were not involved in the creation of this content.